org.apache.hadoop.fs-Seekable

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本来要先看BufferedFSInputStream的，但是它实现了Seekable和PositionedReadable接口，就先看这两个，再看它会比较容易理解些

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package org.apache.hadoop.fs;

import java.io.*;

/** Stream that permits seeking. */
//提供按位置查找功能的接口
public interface Seekable {
  /**
   * Seek to the given offset from the start of the file.
   * The next read() will be from that location.  Can't
   * seek past the end of the file.
   */
  void seek(long pos) throws IOException;
  //从指定文件中的位置pos，对文件流进行前向搜索。
  /**
   * Return the current offset from the start of the file
   */
  long getPos() throws IOException;
//返回文件流中当前偏移位置。 
  /**
   * Seeks a different copy of the data.  Returns true if 
   * found a new source, false otherwise.
   */
  boolean seekToNewSource(long targetPos) throws IOException;
  //从targetPos位置搜索文件数据的一个不同拷贝，搜索到则返回true，否则返回false。
}

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